This application is a 35 USC 371 application of PCT/DE 00/03246 filed on Sep. 19, 2000.
1. Field of the Invention
The invention relates to a method for machining a common rail for a common rail fuel injection system of an internal combustion engine, having a base body, which is equipped with a plurality of connection openings. The invention also relates to a common rail and to a connection stub for application of the method.
2. Description of the Prior Art
In common rail fuel injection systems, a high-pressure pump, optionally with the aid of a prefeed pump, pumps the fuel to be injected out of a tank into the central high-pressure fuel reservoir, which is also called a common rail. From the rail, fuel lines lead to the various injectors that are assigned one to each of the cylinders of the engine. To inject fuel into the combustion chamber of the engine, the injectors are triggered individually by the engine electronics as a function of the engine operating parameters. By means of the common rail, the pressure generation and the injection are decoupled from one another. One conventional common rail is described for instance in German Patent Disclosure DE 195 48 611. The conventional common rail withstands pressures of up to about 1100 bar.
The primary object of the invention is to increase the high-pressure strength of the known common rail by simple provisions.
In a method for machining a common rail for a common rail fuel injection system of an internal combustion engine, having a base body, which is equipped with a plurality of connection openings, this object is attained in that the base body is deformed in the region of the connection openings. Within the context of the present invention, it has been demonstrated that the high-pressure strength of the common rail is limited primarily by the intersections between the connection openings and the base body. In the region of the transitions between the connection openings and the base body, high tensile forces occur during operation. By rounding them off, the transitions between the connection openings and the base body can be made no longer sharp. As a result, the high-pressure strength of the common rail can be enhanced. However, the rounding entails very great effort and high cost. By the mechanical deformation, according to the invention, of the base body, the high-pressure strength of the common rail is enhanced in a much simpler way. The common rail of the invention withstands pressures of over 2000 bar. Advantageously, the provisions according to the invention can be combined with the known provisions, such as rounding the intersections, in order to achieve even better results. The teaching of the invention can also be combined with an eccentric disposition of the connection openings.
A particular embodiment of the method of the invention is characterized in that the base body, in the region of the connection openings, is elastically deformed from outside with the aid of a connection stub. By the mechanical deformation of the base body in the critical region of the intersections, intrinsic pressure stresses are introduced into the region of the intersections. By means of the internal pressure prevailing in the interior of the base body during operation of the common rail, the intrinsic pressure stresses generated in the pressureless state are cancelled out. As a result, the region of the base body that has critical tensile stresses is markedly reduced in size.
In a common rail for application of the method described above, the above-stated object is attained in that in the region of each of the connection openings, one through bore is provided, which has two segments of different-sized internal diameters. By means of the elastic deformation from outside, the bottom of the connection opening, formed by the segment of the through bore having the smaller internal diameter, is deformed inward elastically.
A particular feature of the common rail of the invention is characterized in that a female thread is embodied in the segment of the through bore having the larger internal diameter. The female thread serves to receive a connection stub, which in turn serves to connect high-pressure fuel lines.
In a connection stub for application of the above-described method, the above-stated object is attained in that the outside diameter of the connection stub, on its end toward the common rail, is substantially equal to the internal diameter of the larger diameter segment of the through bore in the common rail. Upon assembly of the connection stub of the invention, the end of the connection stub toward the common rail is pressed against the bottom of the connection opening. As a result, on the one hand the connection opening is sealed off from its surroundings, and on the other, the desired deformation of the bottom of the connection opening is attained.
A particular feature of the connection stub of the invention is characterized in that on the end of the connection stub toward the common rail, a male thread is embodied that is complimentary to the female thread of the through bore. Via the thread, the contact pressure required for the sealing and the deformation is generated. By means of a defined tightening moment and a suitable geometry of the region to be deformed, the magnitude and the direction of the deformation of the critical region of the connection opening can be adjusted.
A further feature of the method of the invention is that in the base body, a rigid internal tube is disposed whose outer contour corresponds to the desired inner contour of the base body in the region of the connection openings, and in that the base body, in the region of the connection openings, is deformed from outside plastically inward with a tool. According to the present invention, the base body is compressed inward in the region of the transitions between the connection openings and the base body. The internal tube serves in a sense as a template for the base body in the region of the connection openings and remains in the base body after the deformation. By the deformation of the base body, the region of the greatest tensile stress is removed from the region of the intersection, which has an advantageous effect on the high-pressure strength of the common rail.
A further feature of the method of the invention is that the internal tube is elastically deformed in the plastic deformation of the base body. In the ideal state, it is attained that the internal tube rests with its full surface against the base body once the deformation is concluded.
A further feature of the method of the invention is that during the deformation of the base body, a mandrel is introduced into the internal tube. With the mandrel, an undesired plastic deformation of the internal tube during the deformation of the base body is avoided.